Download Form Validation - part 5 (writing a custom Form

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Form Validation - part 5 (writing a custom Form Validation
annotation)
Custom Form Validation Annotation
Suppose we have a requirement where we do not have a build in annotation provided for any specific
requirement for you own project than in that case Spring Framework provides Developer to create Custom
Form Validation Annotation and then used this annotation like any other build in annotation in your
application
For Example : Suppose we have a requirement where we want the user to enter hobby from a set of already
defined hobby, for example [skating,music,reading] and if user enters a hobby other than this then our
Application should throw a validation message.
Let see how we can achieve this
Steps to create a Custom Form Validation Annotation with the name - IsValidHobby
1. Create a Java file(called as an annotation type or simply an interface) having complete definition of
this custom annotation like name of the custom annotation,the default error message information etc
2. Create a Java file(a class) - having the validation logic used by the custom annotation to validate the
user input
Code for IsValidHobby.java which has complete defination of the Custom Form Validation @IsValidHobby
that we will be using in our Student.java file
IsValidHobby.java
package com.technicalstack.studentRegistrationController;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.validation.Constraint;
import org.springframework.messaging.handler.annotation.Payload;
@Documented
@Constraint(validatedBy = HobbyValidator.class)
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface IsValidHobby {
String message() default "Please enter a valid hobby "+"Options values are - Skating,Music,Reading(Provide
anyone)";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default{};
}
Here all the code that is in blue colour is mandatory when we write any Custom Form Validator
The message in yellow is the default message that would be displayed on the page.
Code for HobbyValidator.java
package com.technicalstack.studentRegistrationController;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
public class HobbyValidator implements
ConstraintValidator<IsValidHobby,String> {
@Override
public void initialize(IsValidHobby isValidHobby) {
// TODO Auto-generated method stub
}
@Override
public boolean isValid(String studentHobby, ConstraintValidatorContext
ctx) {
if(studentHobby == null){
return false;
}
if(studentHobby.matches("Skating|Music|Reading")){
return true;
}
else{
return false;
}
}
}
Now,we will use the custom validator in our Student.java file as below
@Size(min=3, max=25)@IsValidHobby
private String studentHobby;
Next to test this ,we will run our application and enter a hobby [Traveling] which is not as predefined
one[Skating,Music,Reading] and submit the form.
Our Application will give the expected default error message which we have defined in our
IsValidHobby.java file
Post date: 2016-08-13 10:43:56
Post date GMT: 2016-08-13 10:43:56
Post modified date: 2016-08-13 11:40:45
Post modified date GMT: 2016-08-13 11:40:45
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